Basic Science — FRCS Quiz

13 slides

▸ Slide 1 · Basic scienceBasic Science · 2 questions expand

Question list

Q1-Q22 questions — tap to reveal all answerslist

What is the scope of this introductory basic science slide?
Which basic science topics should be revised from this section?

Answers · Q & A

Q1.What is the scope of this introductory basic science slide?

Not covered in the speaker notes
The slide image is the only source for this slide

Q2.Which basic science topics should be revised from this section?

Not covered in the speaker notes
No topic list is provided in the notes

▸ Slide 2 · Stress strain curveBasic Science · 15 questions expand

Question list

Q1-Q1515 questions — tap to reveal all answerslist

Describe the axes of a stress-strain curve.
Describe the elastic phase of the stress-strain curve.
What is Young's modulus and what does it measure?
Differentiate the proportionality limit, elastic limit and yield stress.
What happens during the plastic phase of a stress-strain curve?
What is strain hardening and how does cold working relate to it?
What is necking and what causes it?
What does the area under the stress-strain curve represent?
Why is annealing performed and what are its three stages?
Give the sequence of Young's modulus of materials.
What is special about the stress-strain behaviour of tendon and ceramic?
Define stiffness, hardness and rigidity.
Define ductility, toughness and strength.
Define notch sensitivity, endurance limit and fatigue life.
Draw and label a stress-strain curve (slide task).

Answers · Q & A

Q1.Describe the axes of a stress-strain curve.

Y axis = stress = force/area (N/m2)
X axis = strain = change in length over original length (no unit/%)
Graph measures tensile stress, but compressive and bending forces relate more to daily use

Q2.Describe the elastic phase of the stress-strain curve.

Proportional change of stress and strain
Slope is Young's modulus, measuring material stiffness
Behaviour follows Hook's law

Q3.What is Young's modulus and what does it measure?

Slope of the elastic phase of the stress-strain curve
Measures material stiffness

Q4.Differentiate the proportionality limit, elastic limit and yield stress.

Proportionality limit: stress at which Hook's law is no longer obeyed
Elastic limit: stress at which deformation stops being entirely reversible (end of elastic phase)
Yield stress: stress needed to induce 0.2% permanent strain (start of plastic phase)

Q5.What happens during the plastic phase of a stress-strain curve?

Yielding represents material bond breakage
The kink: upper and lower yield point due to grain dislocations and relocations, usually in ductile materials
Strain hardening increases resistance to further deformation
Highest point is the ultimate tensile strength (UTS), then necking and breakage

Q6.What is strain hardening and how does cold working relate to it?

Plastic deformation increases a material's resistance to further deformation
Lattice defects become too numerous and restrict each other's movements
Cold working increases the yield point and ultimate tensile strength
At the expense of lower ductility and toughness

Q7.What is necking and what causes it?

Dislocation of molecules after the UTS
Leads to reduction in the cross sectional area
Followed by breakage of the material

Q8.What does the area under the stress-strain curve represent?

Toughness of the material
Energy absorbed per unit area before fracture

Q9.Why is annealing performed and what are its three stages?

Heating above the recrystallisation temperature after cold working, to restore original properties
Stages: recovery, recrystallisation, grain growth
Reduces hardness, making it more workable for further work hardening, and relieves internal stresses
Increases ductility and enhances toughness

Q10.Give the sequence of Young's modulus of materials.

Ceramic, cobalt chrome, stainless steel, titanium, matrix polymers
Then cortical bone, PMMA, PE, cancellous bone, tendon, cartilage

Q11.What is special about the stress-strain behaviour of tendon and ceramic?

Tendon: initial toe phase when collagen fibres align longitudinally to take up stress; fails in a stepwise manner as fibres break sequentially
Ceramic: high Young's modulus with a very short/no plastic phase

Q12.Define stiffness, hardness and rigidity.

Stiffness: ability of a material to resist deformation (slope of a load-displacement curve)
Hardness: resistance of a localised surface to deformation; takes into account stiffness and UTS; not a basic mechanical property
Rigidity: a structure's ability to resist deformation

Q13.Define ductility, toughness and strength.

Ductility: degree of plastic deformation a material can undergo before failure
Toughness: energy per unit volume a material can absorb before failure (from ductility and the UTS)
Strength: maximal stress a material can withstand before fracture

Q14.Define notch sensitivity, endurance limit and fatigue life.

Notch sensitivity: sensitivity to fracture from a surface inhomogeneity (do not mix up with scratch profile)
Endurance limit: stress withstand after 10 million cycles without fatigue failure
Fatigue life: number of cycles needed to cause failure at a specific stress level

Q15.Draw and label a stress-strain curve (slide task).

Label the elastic phase (slope = Young's modulus) and plastic phase
Mark proportionality limit, elastic limit, yield stress, UTS and breakage
Show area under the curve = toughness
Slide asks to draw the curve and give the sequence of Young's modulus, plus tendon and ceramic

▸ Slide 3 · ViscoelasticityBasic Science · 6 questions expand

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Q1-Q66 questions — tap to reveal all answerslist

Define a viscoelastic material.
Compare the behaviour of an elastic solid and a viscous liquid.
Define creep.
Define stress relaxation.
What is the effect of loading rate on stiffness in viscoelastic materials?
What is hysteresis?

Answers · Q & A

Q1.Define a viscoelastic material.

Materials sensitive to the time and rate at which the load is applied

Q2.Compare the behaviour of an elastic solid and a viscous liquid.

Elastic solid: stores all the energy used to deform it
Viscous liquid: dissipates all the energy used to deform it by flow
Viscoelastic materials are intermediate in properties between the two

Q3.Define creep.

Constant stress
Strain increases with time

Q4.Define stress relaxation.

Constant strain
Stress decreases with time

Q5.What is the effect of loading rate on stiffness in viscoelastic materials?

Strain behaviour is time dependent
Stiffness increases with increased rate of loading

Q6.What is hysteresis?

Different stress-strain behaviour upon loading vs unloading
Due to heat dissipated when micromolecules move against each other

▸ Slide 4 · S-N curve: number of cycles leading to fatigue fracture at a specific stressBasic Science · 5 questions expand

Question list

Q1-Q55 questions — tap to reveal all answerslist

What does an S-N curve show?
What do the X and Y axes of the S-N curve represent?
Define the endurance limit and what it divides.
Differentiate brittle fracture, fatigue fracture and creep fracture.
Define fatigue strength/limit.

Answers · Q & A

Q1.What does an S-N curve show?

Number of cycles leading to fatigue fracture at a specific stress
Left side = low cycle fatigue; right side = high cycle fatigue

Q2.What do the X and Y axes of the S-N curve represent?

X axis = number of cycles (N)
Y axis = stress (S)
Plots the number of cycles leading to fatigue fracture at a specific stress

Q3.Define the endurance limit and what it divides.

Stress a material can withstand after 10 million cycles without fatigue failure
Divides finite-life fatigue from infinite-life fatigue

Q4.Differentiate brittle fracture, fatigue fracture and creep fracture.

Brittle fracture: stress > UTS, single load
Fatigue fracture: below UTS, above endurance limit, repetitive load
Creep fracture: below UTS, above yield strength, constant load with time; fails when stretched out

Q5.Define fatigue strength/limit.

Stress at which fracture occurs after a specified number of loading cycles
Contrast with the endurance limit, defined at 10 million cycles

▸ Slide 5 · Progress of fatigue fractureBasic Science · 3 questions expand

Question list

Q1-Q33 questions — tap to reveal all answerslist

List the 3 zones of a fatigue fracture.
What are ratchet marks and how do they form?
What are beach marks and when are they absent?

Answers · Q & A

Q1.List the 3 zones of a fatigue fracture.

1. Crack initiation zone
2. Fatigue zone (beach marks)
3. Instantaneous zone

Q2.What are ratchet marks and how do they form?

Formed when multiple fatigue origins are near each other
A crack starts at each origin; as cracks meet, a ridge or step is formed
Ratchet marks are not origins, but the location where cracks meet

Q3.What are beach marks and when are they absent?

Alternating stripes of lighter and darker colour in the fatigue zone
Colours result from different loading levels or environmental conditions
Absent when cracks grow under uniform loading and environmental conditions

▸ Slide 6 · Photo showing wear in inner surface of femoral head and base of trunnion of femoBasic Science · 9 questions expand

Question list

Q1-Q99 questions — tap to reveal all answerslist

Define corrosion and list the types shown.
Describe galvanic corrosion.
Describe crevice corrosion.
Describe pitting corrosion.
What is fretting corrosion?
What is stress corrosion?
What is the trunnion and how is it designed?
How can corrosion be reduced?
How is wear classified and where was wear seen in the photo?

Answers · Q & A

Q1.Define corrosion and list the types shown.

Destruction of material due to electrochemical reaction
Galvanic, crevice, pitting, fretting and stress corrosion

Q2.Describe galvanic corrosion.

Occurs with 2 dissimilar metals electrically coupled
Difference in surface potential causes electron transfer from one metal to another

Q3.Describe crevice corrosion.

A cavity is shielded off from the rest of the fluid
Causes build-up of reactive species and decreased pH and O2 tension

Q4.Describe pitting corrosion.

Pit from abrasion
Then corrosion and material exposed
Repeating cycle

Q5.What is fretting corrosion?

Micromotion between two materials; combination of wear and corrosion
Destruction of the oxide film

Q6.What is stress corrosion?

Initial crack, then corrosion sets in
Repeated mechanical loading causes fracture

Q7.What is the trunnion and how is it designed?

Trunnion = shape of the proximal end of the modular femoral stem connecting with the femoral head
Designed to be side bearing
-ve/+ve mismatch in different manufacturers
Side angle around 5-6 degrees; total <12 degrees = stable

Q8.How can corrosion be reduced?

Material: choose a corrosion-resistant material, treat surface with passivation
Construct: monoblock, careful technique to prevent surface scratching
Do not use different metals in close vicinity

Q9.How is wear classified and where was wear seen in the photo?

Wear divided into mechanical or chemical wear
Likely chemical wear = corrosion in this region
Photo shows wear on the inner surface of the femoral head and base of the trunnion of the femoral stem

▸ Slide 7 · Antibiotics containing acrylic beadsBasic Science · 4 questions 1 check expand

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Q1-Q44 questions — tap to reveal all answerslist

What are antibiotic-containing acrylic beads made of?
What are the advantages of antibiotic beads?
What is the size and gentamicin content of each bead?
Why is gentamicin suitable for antibiotic beads?

Answers · Q & A

Q1.What are antibiotic-containing acrylic beads made of?

PMMA cement loaded with gentamicin sulphate
Zirconium dioxide contrast medium, threaded on a metal wire

Q2.What are the advantages of antibiotic beads?

High localised antibiotic concentration without systemic side effects
Reduce dead space

Q3.What is the size and gentamicin content of each bead?

Each bead is 7mm in diameter
Contains 7.5g gentamicin per the speaker notes

Q4.Why is gentamicin suitable for antibiotic beads?

Broad-spectrum aminoglycoside, effective against gram +ve and gram -ve bacteria
Bactericidal, heat stable and soluble
Low rate of resistance and allergy
Low MIC (minimal concentration in situ to inhibit bacterial growth)

Fact check

Each antibiotic bead is 7mm and contains 7.5g gentamicin — Unit error: grams should be milligrams — Septopal PMMA beads are 7mm diameter and contain gentamicin in milligram amounts (reported around 4.5-7.5 mg per bead), not 7.5 g — source

▸ Slide 8 · Free body diagramBasic Science · 8 questions expand

Question list

Q1-Q88 questions — tap to reveal all answerslist

Define joint reaction force, instant centre of rotation and centre of gravity.
State Newton's laws and the definition of a Newton.
Define vector, scalar, moment, work and energy.
What are the assumptions of free body analysis at a joint?
How can you reduce the joint reaction force at the hip?
Give the lever class for shoulder, elbow, hip, ankle, MTPJ and spine.
What is the advantage of a class 3 lever?
Which free body diagram exercises are listed on this slide?

Answers · Q & A

Q1.Define joint reaction force, instant centre of rotation and centre of gravity.

JRF: force generated within a joint in response to forces acting on the joint
Instant centre of rotation: point about which a joint rotates
Centre of gravity: just anterior to S2

Q2.State Newton's laws and the definition of a Newton.

First law: no net force = velocity constant
Second law: F = ma
Third law: equal and opposite reaction (F2 = -F1)
1 Newton = force to give 1 kg an acceleration of 1 m/s2

Q3.Define vector, scalar, moment, work and energy.

Vector: quantity with direction and magnitude; scalar: no direction
Moment (torque) = force (perpendicular) x distance
Work = force (vector parallel to displacement) x distance
Energy = ability of an object to perform work

Q4.What are the assumptions of free body analysis at a joint?

Static equilibrium and rigid fulcrum (bone)
Frictionless joint and no antagonist muscle action
Simple hinge lever, force in a single direction, line of action at the muscle centre

Q5.How can you reduce the joint reaction force at the hip?

Reduce body weight
Body tilt (antalgic gait tilts towards the painful side to reduce the BW moment arm)
Contralateral stick
Increase the abductor moment arm
Ipsilateral suitcase helps the abductors

Q6.Give the lever class for shoulder, elbow, hip, ankle, MTPJ and spine.

Shoulder 3, elbow 3
Hip 1, spine 1
Ankle 1 (or 2 if the MTPJ is the fulcrum)
MTPJ 2

Q7.What is the advantage of a class 3 lever?

Larger range of movement
Hence seen in the upper limb

Q8.Which free body diagram exercises are listed on this slide?

Draw FB diagrams of the ankle/MTPJ/knee/hip/shoulder/elbow/spine
Show with a FB diagram how RSA helps deltoid function
Explain with a FB diagram why kneeling increases PFJ pressure
The notes list these as exercises but give no answers

▸ Slide 9 · Explain why proximal migration of humeral head in rotator cuff arthropathy with FB diagram.Basic Science · 2 questions expand

Question list

Q1-Q22 questions — tap to reveal all answerslist

Why does the humeral head migrate proximally in rotator cuff arthropathy?
On the free body diagram, which force becomes unopposed once the cuff fails?

Answers · Q & A

Q1.Why does the humeral head migrate proximally in rotator cuff arthropathy?

Loss of supraspinatus and loss of downward coupling
Excessive upward pull of the humerus

Q2.On the free body diagram, which force becomes unopposed once the cuff fails?

The deltoid's upward pull on the humerus
Normally balanced by the cuff's downward coupling force, so its loss causes proximal migration of the humeral head

▸ Slide 10 · TribologyBasic Science · 3 questions expand

Question list

Q1-Q33 questions — tap to reveal all answerslist

Define tribology.
Define friction.
Define wear and what it depends on.

Answers · Q & A

Q1.Define tribology.

Study of interacting surfaces
Specifically surfaces in relative motion

Q2.Define friction.

Resistance to movement between two surfaces in contact
= load between surfaces x coefficient of friction

Q3.Define wear and what it depends on.

Removal of material from two surfaces under load due to the sliding motion between them
Depends on load, sliding distance and material property

▸ Slide 11 · Stribeck curveBasic Science · 2 questions expand

Question list

Q1-Q22 questions — tap to reveal all answerslist

What is the Hersey number?
What does the Stribeck curve show?

Answers · Q & A

Q1.What is the Hersey number?

Viscosity x speed / load
Used with the Stribeck curve to relate friction to these variables

Q2.What does the Stribeck curve show?

Relationship of friction to movement speed (head size) and viscosity of lubricant
Also shows the effect of load on the bearing surface

▸ Slide 12 · Clotting profileBasic Science · 3 questions expand

Question list

Q1-Q33 questions — tap to reveal all answerslist

How are the intrinsic and extrinsic clotting pathways activated?
How do LMWH/heparin work?
Match dabigatran, rivaroxaban and warfarin to their targets.

Answers · Q & A

Q1.How are the intrinsic and extrinsic clotting pathways activated?

Intimal tear -> exposed collagen -> activates the intrinsic pathway
Damage of vessels -> exposes extravascular tissue -> activates the extrinsic pathway

Q2.How do LMWH/heparin work?

Activate antithrombin 3
Antithrombin 3 inhibits factor 2 and factor 10

Q3.Match dabigatran, rivaroxaban and warfarin to their targets.

Dabigatran: inhibits factor 2 (Bi = 2)
Rivaroxaban: factor 10a inhibitor (Xa = 10a)
Warfarin: inhibits factors 2, 7, 9, 10 via vitamin K epoxide reductase inhibition

▸ Slide 13Basic Science · 2 questions expand

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